Blocks are used for pathing. Making a box just for stalling monsters is not advised. When placing blocks, keep these things in mind: If you have a single strong block next to a few weak blocks, monsters will simply go around the strong block and attack the weak blocks to get through. This means that the strong block never served its purpose. Make sure to build a wall of blocks of the same level in order to best channel the monsters into Booby Traps and away from your resources. Booby traps should be used with blocks as monsters go through gaps in a wall, a booby trap will destroy monsters before they even get close. However, it is a good idea to place more than 1 booby trap as more advanced players will take out booby traps with low level monsters e.g Pokies. Moreover Octo-ooze, Eye-ra, Ichi and level 6 locker level 3 and 4 monsters can survive damage taken from booby traps.
Try placing your blocks in front of defensive towers, giving them more time to attack the monster while the block is being destroyed as a decoy. Another effective use of blocks is to lead monsters into certain areas away from your resource towers, or straight into areas with traps or great CF. A lvl.1 Gorgo and Drull can destroy a lvl.1 block in one hit so it is best to upgrade your blocks as soon as possible.